Reciprocating linear-motion pumps for liquid or pasty products and which are mechanically connected to electric motor control systems are known. Such linear pumps are driven with a predetermined stroke, after which the direction of travel is reversed, and the pump is driven over the same predetermined stroke in the opposite direction. The movement of the pump piston can be reversed from a direction of expelling the component to a direction of drawing in and expelling the component, and vice versa. The pump circuit comprises an intake valve and a delivery valve both associated with the pump.
The reversal of the direction of travel of the pump causes a sudden drop in pressure followed immediately by a pressure spike in the flow of the liquid or pasty product delivered by the pump. When the direction of travel of the pump is reversed, the valves that hold back the liquid or pasty product in a reciprocating-motion pump may also contribute to the pressure variations that occur during reversal.
Electric-motor-powered drive systems for linear reciprocating-motion pumps and comprising electrical controls for regulating the speed at which the motor is driven according to the pressure or delivery of liquid or pasty product, with electric cut-off means for disconnecting the supply of power to the motor when pressure lock conditions are encountered, are known.
The reversal effect is, however, amplified by the inertia of an electric-motor-drive device connected mechanically to a reciprocating linear-motion double-acting pump, generating a pressure drop which is longer and a pressure spike that is higher during reversal.